<!DOCTYPE html>
<html lang="en">
	<head>
	<title>three.js webgl - buffergeometry - selective - draw</title>
	<meta charset="utf-8">
	<meta name="viewport" content="width=device-width, user-scalable=no, minimum-scale=1.0, maximum-scale=1.0">
	<link type="text/css" rel="stylesheet" href="main.css">

	<script type="x-shader/x-vertex" id="vertexshader">
		attribute float visible;
		varying float vVisible;
		attribute vec3 vertColor;
		varying vec3 vColor;

		void main() {

			vColor = vertColor;
			vVisible = visible;
			gl_Position = projectionMatrix * modelViewMatrix * vec4( position, 1.0 );

		}
	</script>
	<script type="x-shader/x-fragment" id="fragmentshader">
		varying float vVisible;
		varying vec3 vColor;

		void main() {

			if ( vVisible > 0.0 ) {

				gl_FragColor = vec4( vColor, 1.0 );

			} else {

				discard;

			}

		}
	</script>
	</head>
	<body>
		<div id="info">
			<a href="https://threejs.org" target="_blank" rel="noopener">three.js</a> buffergeometry - selective - draw
			<div id="title"></div>
			<div id="ui"><a href="#" id="hideLines">CULL SOME LINES</a> - <a href="#" id="showAllLines">SHOW ALL LINES</a></div>
		</div>

		<script type="importmap">
			{
				"imports": {
					"three": "../build/three.module.js",
					"three/addons/": "./jsm/"
				}
			}
		</script>

		<script type="module">

			import * as THREE from 'three';

			import Stats from 'three/addons/libs/stats.module.js';

			let camera, scene, renderer, stats;
			let geometry, mesh;
			const numLat = 100;
			const numLng = 200;
			let numLinesCulled = 0;

			init();

			function init() {


				scene = new THREE.Scene();

				camera = new THREE.PerspectiveCamera( 45, window.innerWidth / window.innerHeight, 0.01, 10 );
				camera.position.z = 3.5;

				stats = new Stats();
				document.body.appendChild( stats.dom );

				window.addEventListener( 'resize', onWindowResize );

				addLines( 1.0 );

				const hideLinesButton = document.getElementById( 'hideLines' );
				hideLinesButton.addEventListener( 'click', hideLines );

				const showAllLinesButton = document.getElementById( 'showAllLines' );
				showAllLinesButton.addEventListener( 'click', showAllLines );

				renderer = new THREE.WebGLRenderer( { antialias: true } );
				renderer.setPixelRatio( window.devicePixelRatio );
				renderer.setSize( window.innerWidth, window.innerHeight );
				renderer.setAnimationLoop( animate );
				document.body.appendChild( renderer.domElement );

			}

			function addLines( radius ) {

				geometry = new THREE.BufferGeometry();
				const linePositions = new Float32Array( numLat * numLng * 3 * 2 );
				const lineColors = new Float32Array( numLat * numLng * 3 * 2 );
				const visible = new Float32Array( numLat * numLng * 2 );

				for ( let i = 0; i < numLat; ++ i ) {

					for ( let j = 0; j < numLng; ++ j ) {

						const lat = ( Math.random() * Math.PI ) / 50.0 + i / numLat * Math.PI;
						const lng = ( Math.random() * Math.PI ) / 50.0 + j / numLng * 2 * Math.PI;

						const index = i * numLng + j;

						linePositions[ index * 6 + 0 ] = 0;
						linePositions[ index * 6 + 1 ] = 0;
						linePositions[ index * 6 + 2 ] = 0;
						linePositions[ index * 6 + 3 ] = radius * Math.sin( lat ) * Math.cos( lng );
						linePositions[ index * 6 + 4 ] = radius * Math.cos( lat );
						linePositions[ index * 6 + 5 ] = radius * Math.sin( lat ) * Math.sin( lng );

						const color = new THREE.Color( 0xffffff );

						color.setHSL( lat / Math.PI, 1.0, 0.2 );
						lineColors[ index * 6 + 0 ] = color.r;
						lineColors[ index * 6 + 1 ] = color.g;
						lineColors[ index * 6 + 2 ] = color.b;

						color.setHSL( lat / Math.PI, 1.0, 0.7 );
						lineColors[ index * 6 + 3 ] = color.r;
						lineColors[ index * 6 + 4 ] = color.g;
						lineColors[ index * 6 + 5 ] = color.b;

						// non-0 is visible
						visible[ index * 2 + 0 ] = 1.0;
						visible[ index * 2 + 1 ] = 1.0;

					}

				}

				geometry.setAttribute( 'position', new THREE.BufferAttribute( linePositions, 3 ) );
				geometry.setAttribute( 'vertColor', new THREE.BufferAttribute( lineColors, 3 ) );
				geometry.setAttribute( 'visible', new THREE.BufferAttribute( visible, 1 ) );

				geometry.computeBoundingSphere();

				const shaderMaterial = new THREE.ShaderMaterial( {

					vertexShader: document.getElementById( 'vertexshader' ).textContent,
					fragmentShader: document.getElementById( 'fragmentshader' ).textContent
				} );

				mesh = new THREE.LineSegments( geometry, shaderMaterial );
				scene.add( mesh );

				updateCount();

			}

			function updateCount() {

				const str = '1 draw call, ' + numLat * numLng + ' lines, ' + numLinesCulled + ' culled (<a target="_blank" href="http://callum.com">author</a>)';
				document.getElementById( 'title' ).innerHTML = str.replace( /\B(?=(\d{3})+(?!\d))/g, ',' );

			}

			function hideLines() {

				for ( let i = 0; i < geometry.attributes.visible.array.length; i += 2 ) {

					if ( Math.random() > 0.75 ) {

						if ( geometry.attributes.visible.array[ i + 0 ] ) {

							++ numLinesCulled;

						}

						geometry.attributes.visible.array[ i + 0 ] = 0;
						geometry.attributes.visible.array[ i + 1 ] = 0;

					}

				}

				geometry.attributes.visible.needsUpdate = true;

				updateCount();

			}

			function showAllLines() {

				numLinesCulled = 0;

				for ( let i = 0; i < geometry.attributes.visible.array.length; i += 2 ) {

					geometry.attributes.visible.array[ i + 0 ] = 1;
					geometry.attributes.visible.array[ i + 1 ] = 1;

				}

				geometry.attributes.visible.needsUpdate = true;

				updateCount();

			}

			function onWindowResize() {

				camera.aspect = window.innerWidth / window.innerHeight;
				camera.updateProjectionMatrix();

				renderer.setSize( window.innerWidth, window.innerHeight );

			}

			function animate() {

				const time = Date.now() * 0.001;

				mesh.rotation.x = time * 0.25;
				mesh.rotation.y = time * 0.5;

				renderer.render( scene, camera );

				stats.update();

			}

		</script>
	</body>
</html>
